Various automated optical inspection (AOI) systems are commercially available to inspect electrical circuits, such as printed circuit boards, during manufacture to detect defects. Some AOI systems acquire an image of an electrical circuit to be inspected with reflected monochromatic or polychromatic light. Reflected light AOI systems include the Inspire™, Spiron™ and InFinex™ AOI systems available from Orbotech Ltd. of Yavne, Israel. Other AOI systems acquire an image of an electrical circuit to be inspected from a fluorescence response to a scanned laser beam. Scanning laser AOI systems include the Vision™ AOI system also available from Orbotech Ltd. of Yavne, Israel.
In order to ensure that all defects on an electrical circuit are detected, AOI systems are adjusted to produce a detection result sufficiently sensitive to detect all real defects. Such a level of sensitization also results in some non-defective locations being falsely identified as including a defect. Accordingly, after inspection defects identified during AOI are verified in a downstream verification operation to confirm whether the defect is indeed a real defect, or rather a false call.